Update getting started guide, example script

[mattwthompson]

• Update "getting started" section
  • Add bit about grabbing data from QCSubmit
• Add usage examples
  • Get molecule identifiers
  • Inspect QM and MM structures
  • Manually compute DDE

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.50%. Comparing base (216c208) to head (d92edb2).
Report is 31 commits behind head on yammbs-models.

Additional details and impacted files

[ntBre]

This looks great overall. I added some suggested fixes to very minor typos but otherwise happy to approve. I think the model_validate_json question I marked is the only potentially-functional issue, but if the script runs then it's clearly not a problem.

[mattwthompson]

Thanks for the review @ntBre! I will try to finish this up later today